1. Field of the Invention
The present invention relates to methods for processing semiconductor substrates and the semiconductor substrates, and particularly to a semiconductor substrate processing method and a semiconductor substrate in which formation of dust particles from the edge part of the substrate is prevented.
2. Description of the Background Art
While SOI (Silicon On Insulator) devices in which semiconductor elements are formed on SOI substrates are superior to bulk devices in their reduced junction capacitance and improved element isolation breakdown voltage, the SOI devices have their unique problems as described below.
FIG. 32 shows a partial cross-section of an SOI substrate 10. The SOI substrate 10 includes a buried oxide film 2 and a single-crystal silicon layer (hereinafter referred to as an SOI layer) 1 sequentially stacked in the upper main surface of a single-crystal silicon substrate 3.
SOI substrate manufacturing methods include an SIMOX (Separation by Implanted Oxygen) method and a bonding method, for example. The SOI substrate 10 shown in FIG. 32 is manufactured by the SIMOX method.
In the SIMOX method, an SOI structure is obtained by implanting oxygen ions into a single-crystal silicon substrate to doses of 1xc3x971018 to 2xc3x971018/cm2 at 150 to 200 KeV and then annealing it at about 1300 to 1400xc2x0 C., for example.
FIG. 32 shows the edge part of the SOI substrate 10 in detail. In the following description, a semiconductor substrate is referred to separately in its upper main surface (the side on which semiconductor elements are formed), center part thereof (the part including the active region), edge part including the peripheral part around the center part and the side part, and lower main surface.
As shown in FIG. 32, the edge part is curved with a large curvature. Accordingly, when oxygen ions are implanted there from the vertical direction, the oxygen ions are obliquely implanted, so that the effective implantation energy is reduced. As a result, the buried oxide film 2 and the SOI layer 1 are thinner in the edge part. Further, the surface of the edge part is not smooth but rough with irregularities. This phenomenon is general with silicon substrates formed by CZ (Czochralski) method. In the irregular part, the SOI layer 1 may be so thin that the buried oxide film 2 is exposed. In this condition, the SOI layer 1 is prone to exfoliation.
In addition, the film-thinning process for the SOI layer 1 performed in the SOI device manufacturing process facilitates the exfoliation of the SOI layer 1. The film-thinning process for the SOI layer 1 will now be described.
The SOI layer 1 in the SOI substrate 10 is formed to an approximate thickness at the time of production of the substrate. The film-thinning process for the SOI layer 1 is performed to appropriately reduce the thickness of the SOI layer 1 according to specifications of desired semiconductor devices. In this process, the thickness of the SOI layer 1 is adjusted by oxidizing the SOI layer 1.
The thickness of an oxide film formed on the SOI layer is generally determined on the basis of the thickness of the SOI layer 1 in the center part of the SOI substrate 10, or in the semiconductor element formation region (active region). In this process, the thin SOI layer 1 in the edge part of the SOI substrate 10 presents the problem as stated above. The buried oxide film 2 may be exposed in some parts.
FIG. 33 is a schematic diagram showing the region X in FIG. 32. As shown in FIG. 33, the buried oxide film 2 is also irregular in the edge part of the SOI substrate 10, reflecting the shape of the irregular part DP of the SOI layer 1. Since oxygen ions are implanted from the vertical direction, the irregularities on the SOI layer 1 and the irregularities on the buried oxide film 2 are formed in shifted positions, which may cause the buried oxide film 2 to be exposed.
Next, FIG. 34 shows the SOI layer 1 and an oxide film OX formed thereon to thin the SOI layer 1. As the formation of the oxide film OX thins the SOI layer 1, the oxide film OX may be coupled to the buried oxide film 2 or the SOI layer 1 may be completely oxidized in the edge part. In such a case, the SOI layer 1 may be partially surrounded by the buried oxide film 2 and the oxide film OX. For example, the part 1A of the SOI layer shown in FIG. 34 is surrounded by the oxide film OX and the buried oxide film 2.
When the SOI substrate 10 is wet-etched in this condition with an etching solution, such as hydrofluoric acid (HF), to remove the oxide film OX, the buried oxide film 2 will be etched away together with the oxide film OX, as shown in FIG. 35. Then, the SOI layer 1A will be lifted off to be a particle, which will be suspended in the etching solution and may adhere to the center part of the SOI substrate 10. If particles adhere to the semiconductor element formation region, it will cause defective formation of semiconductor elements to reduce the production yield.
In some cases, a polysilicon layer may be formed on the edge part and the lower main surface of the silicon substrate 3 for gettering of contaminants like heavy metals taken in the wafer manufacturing process or in the wafer process for transistors. In this case, the SOI layer 1 and the buried oxide layer 2 become uneven due to polycrystallinity of the polysilicon layer, and the SOI layer 1 will then partially come off to be particles, similarly to the phenomenon described above.
Particles may be produced also with SOI substrates formed by a bonding method (bonded substrates).
With a bonded substrate, the SOI structure is obtained by forming an oxide film on the upper main surface (on the main surface on which semiconductor elements are formed) of a silicon substrate 3, bonding another silicon substrate thereon, and polishing that silicon substrate to a desired thickness. FIG. 36 shows a cross-section of the edge part of an SOI substrate 20 formed this way.
In FIG. 36, an on-substrate oxide film 6 and a silicon layer 7 are placed on top of the other on the upper main surface of the silicon substrate 3 to form an SOI structure. The on-substrate oxide film 6 corresponds to the buried oxide film and the silicon layer 7 to the SOI layer.
With the SOI substrate 20 having this structure, the on-substrate oxide film 6 is exposed in the edge part. Hence, etching solution used in wet-etching may invade the exposed part to partially remove the on-substrate oxide film 6, causing the silicon layer 7 to be partially hung as shown in FIG. 37. In this condition, the silicon layer 7 is prone to come off to be a particle.
When the edge part of the on-substrate oxide film 6 and the silicon layer 7 is imperfectly beveled, the periphery will show continuous irregularities in a plane view. The irregular part may come off in transportation of the substrate to produce particles.
As described above, conventional semiconductor substrates, particularly SOI substrates produced by the SIMOX method have the problem that the SOI layers in the edge part of the substrates may come off to be particles, to reduce the production yield. Particles may be produced also with SOI substrates manufactured by the bonding method.
A first aspect of the present invention is directed to a method for processing a semiconductor substrate having a first main surface, a second main surface on the opposite side, and a side part, wherein a part where an active region is formed in the first main surface is defined as a center part, and a part including a peripheral region around the center part in the first main surface and the side part is defined as an edge part. According to the present invention, the semiconductor substrate is an SOI substrate formed by an SIMOX method, and the semiconductor substrate comprises a buried oxide film and an SOI layer formed in the first main surface in a sequentially stacked form, the method comprising a silicon-ion implantation step wherein silicon ions are implanted into the edge part to eliminate the buried oxide film formed in the edge part.
Preferably, according to a second aspect of the present invention, in the semiconductor substrate processing method, the silicon ion implantation step comprises the step of implanting the silicon ions from the side of the edge part in a direction of a radius of the SOI substrate.
Preferably, according to a third aspect of the present invention, in the semiconductor substrate processing method, the silicon ion implantation step comprises the step of forming an implant mask in the center part of the first main surface and then implanting the silicon ions from the side of the edge part and from the side of the first main surface of the SOI substrate.
A fourth aspect of the present invention is directed to a method for processing a semiconductor substrate having a first main surface, a second main surface on the opposite side, and a side part, wherein a part where an active region is formed in the first main surface is defined as a center part, and a part including a peripheral region around the center part in the first main surface and the side part is defined as an edge part. According to the fourth aspect, the semiconductor substrate processing method comprises the steps of (a) forming an insulating film to cover the edge part of the semiconductor substrate, (b) implanting oxygen ions from the side of the first main surface of the semiconductor substrate comprising the insulating film to form a buried oxide film and an SOI layer in a sequentially stacked form in the first main surface by an SIMOX method, and (c) removing the insulating film, thereby forming an SOI substrate having the buried oxide film extending in parallel with the main surface to the outermost end of the edge part.
Preferably, according to a fifth aspect of the present invention, in the semiconductor substrate processing method, the insulating film is formed to a thickness, in its thickest part, equal to or larger than a total thickness of the buried oxide film and the SOI layer, and the step (a) comprises the step of forming a thermal oxide film by a thermal oxidation method as the insulating film.
Preferably, according to a sixth aspect of the present invention, in the semiconductor substrate processing method, the insulating film is formed to a thickness, in its thickest part, equal to or larger than a total thickness of the buried oxide film and the SOI layer, and the step (a) comprises the step of forming a TEOS film by a low pressure CVD method as the insulating film.
A seventh aspect of the present invention is directed to a method for processing a semiconductor substrate having a first main surface, a second main surface on the opposite side, and a side part, wherein a part where an active region is formed in the first main surface is defined as a center part, and a part including a peripheral region around the center part in the first main surface and the side part is defined as an edge part. According to the seventh aspect of the present invention, the semiconductor substrate processing method comprises the steps of (a) applying a first oxygen-ion implantation from the side of the first main surface of the semiconductor substrate all over the surface, (b) selectively applying a second oxygen-ion implantation into the edge part from the side of the first main surface of the semiconductor substrate, and (c) applying an annealing processing to diffuse the oxygen ions implanted by the first and second oxygen-ion implantations to form a buried oxide film and a protective oxide film respectively in the center part and in the edge part and also to form an SOI layer on the buried oxide film, wherein the second oxygen-ion implantation has its implant peak set at a shallower position than that in the first oxygen-ion implantation, and the protective oxide film is formed in the edge part on at least the side of the first main surface from the surface to the inside.
Preferably, according to an eighth aspect of the present invention, in the semiconductor substrate processing method, the step (c) comprises the steps of applying a first annealing processing prior to the step (b) to form the buried oxide film and the SOI layer, and applying a second annealing processing after the step (b) to form the protective oxide film.
According to a ninth aspect of the present invention, a semiconductor substrate processing method comprises the steps of: (a) forming by a bonding method a stacked structure comprising a first semiconductor substrate, an on-substrate oxide film, and a second semiconductor substrate having an outside dimension larger than that of the on-substrate oxide film, the on-substrate oxide film and the second semiconductor substrate being sequentially stacked on a main surface of the first semiconductor substrate, (b) pressing down the second semiconductor substrate from above to bring a main surface of the second semiconductor substrate protruding over the main surface of the first semiconductor substrate into contact with the main surface of the first semiconductor substrate and bonding the first and second semiconductor substrates by a bonding method; and (c) polishing the second semiconductor substrate to a predetermined thickness to form an SOI layer.
A tenth aspect of the present invention is directed to a semiconductor substrate having a first main surface, a second main surface oil the opposite side, and a side part, wherein a part where an active region is formed in the first main surface is defined as a center part, and a part including a peripheral region around the center part in the first main surface and the side part is defined as an edge part. According to the tenth aspect, the semiconductor substrate comprises: a buried oxide film and an SOI layer formed in the first main surface in a sequentially stacked form; a doped polysilicon layer formed in the edge part to cover the edge part; and a protective oxide film formed in said doped polysilicon layer on at least the side of the first main surface from the surface to the inside.
Preferably, according to an eleventh aspect of the present invention, in the semiconductor substrate, a thickness of the doped polysilicon layer in its thickest part in the edge part is equal to or larger than a total thickness of the buried oxide film and the SOI layer, and the doped polysilicon layer is formed also on the second main surface.
The present invention includes a method for processing a semiconductor substrate having one main surface, the other main surface on the opposite side, and a side part, wherein a part where an active region is formed in the one main surface is defined as a center part, and a part including a peripheral region around the center part in the one main surface and the side part is defined as an edge part, the semiconductor substrate processing method comprising the steps of: (a) forming a doped polysilicon layer to cover the edge part of the semiconductor substrate; and (b) implanting oxygen ions from the side of the one main surface of the semiconductor substrate having the doped polysilicon layer to form a buried oxide film and an SOI layer in a sequentially stacked form in the one main surface by an SIMOX method and also to form a protective oxide film in the doped polysilicon layer on at least the side of the one main surface from the surface to the inside.
The present invention is directed to the semiconductor substrate processing method, wherein the doped polysilicon layer is formed to a thickness, in its thickest part in the edge part, equal to or larger than a total thickness of the buried oxide film and the SOI layer, and wherein the step (a) comprises the step of forming the doped polysilicon layer also on the other main surface of the semiconductor substrate.
The present invention includes a method for processing a semiconductor substrate having one main surface, the other main surface on the opposite side, and a side part, wherein a part where an active region is formed in the one main surface is defined as a center part, and a part including a peripheral region around the center part in the one main surface and the side part is defined as an edge part, wherein the semiconductor substrate is an SOI substrate formed by an SIMOX method, and the semiconductor substrate comprises a buried oxide film and an SOI layer sequentially stacked in the one main surface, and wherein a laser beam is applied to the edge part from above in a vacuum to mix the SOI layer and the buried oxide film to form a molten layer in the edge part on the side of the one main surface at least.
The present invention includes a method for processing a semiconductor substrate having an on-substrate oxide film and an SOI layer sequentially stacked on one main surface of the semiconductor substrate, comprising the step of applying a laser beam from above to an edge part of the on-substrate oxide film and the SOI layer in a vacuum to mix the SOI layer and the on-substrate oxide film to form a molten layer in the edge part.
The present invention includes a semiconductor substrate having one main surface, the other main surface on the opposite side, and a side part, wherein a part where an active region is formed in the one main surface is defined as a center part, and a part including a peripheral region around the center part in the one main surface and the side part is defined as an edge part, the semiconductor substrate comprising, a buried oxide film and an SOI layer formed in the one main surface in a sequentially stacked form, and a protective oxide film formed in the edge part on at least the side of the one main surface from the surface to the inside.
The present invention includes semiconductor substrate having one main surface, the other main surface on the opposite side, and a side part, wherein a part where an active region is formed in the one main surface is defined as a center part, and a part including a peripheral region around the center part in the one main surface and the side part is defined as an edge part, the semiconductor substrate comprising, a buried oxide film and an SOI layer formed in the one main surface in a sequentially stacked form, and a molten layer formed by mixing the SOI layer and the buried oxide film in the edge part on the side of the one main surface at least.
The present invention includes a semiconductor substrate comprising an on-substrate oxide film and an SOI layer sequentially stacked on one main surface of the semiconductor substrate, which comprises a molten layer formed by mixing the SOI layer and the on-substrate oxide film in at least an edge part of the on-substrate oxide film and the SOI layer to cover the edge part.
The present invention includes a semiconductor substrate comprising an on-substrate oxide film and an SOI layer sequentially stacked on one main surface of the semiconductor substrate, which comprises an epitaxial layer formed on at least an edge part of the on-substrate oxide film and the SOI layer to cover the edge part.
According to the semiconductor substrate processing method of the first aspect of the present invention, the buried oxide film disappears in the edge part. In the process of thinning the SOI layer, for example, this prevents the problem that the SOI layer in the edge part is partially surrounded by the buried oxide film and an oxide film formed for the thinning process, partially lifted off in removal of the oxide film to be particles, and suspended in etching solution. This prevents defective formation of semiconductor elements due to the presence of particles, leading to improved production yield.
According to the semiconductor substrate processing method of the second aspect of the present invention, it is possible to eliminate the buried oxide film formed in the edge part only by an ion implantation from a single direction. This method is efficient and suppresses an increase in production cost due to the application of the invention.
According to the semiconductor substrate processing method of the third aspect of the present invention, it is possible to eliminate the buried oxide film not only in the edge part but also in a desired region in the center part. This allows the buried oxide film to be absent in a large region.
According to the semiconductor substrate processing method of the fourth aspect of the present invention, the buried oxide film extends to the outermost end of the edge in parallel with the main surface. Hence, a thin SOI layer is not formed on the buried oxide film in the edge part. In the process of thinning the SOI layer, for example, this prevents the problem that a thin SOI layer 1 is partially surrounded by the buried oxide film and an oxide film formed for the thinning process, partially lifted off in removal of the oxide film to be particles, and suspended in etching solution. This prevents defective formation of semiconductor elements due to the presence of particles, leading to improved production yield.
According to the semiconductor substrate processing method of the fifth aspect of the present invention, the thickness of the thickest part of the insulating film is set to be equal to or larger than the total thickness of the buried oxide film and the SOI layer so that the curved part of the buried oxide film is formed inside the insulating film. This prevents formation of the curved part of the buried oxide film in the edge part of the semiconductor substrate. Further, since the insulating film is formed as a thermal oxide film, it can easily be obtained with a suppressed increase in production cost due to the application of the invention.
According to the semiconductor substrate processing method of the sixth aspect of the present invention, the thickness of the thickest part of the insulating film is set to be equal to or larger than the total thickness of the, buried oxide film and the SOI layer so that the curved part of the buried oxide film is formed inside the insulating film. This prevents formation of the curved part of the buried oxide film in the edge part of the semiconductor substrate. Further, the insulating film is formed as a TEOS film, a good insulating film having less pinholes.
According to the semiconductor substrate processing method of seventh aspect of the present invention, a protective oxide film is formed in the edge part on, at least, the first main surface side from the surface to the inside. This prevents formation of a thin SOI layer on the buried oxide film in the edge part. In the process of thinning the SOI layer, for example, this prevents the problem that a thin SOI layer is partially surrounded by the buried oxide film and an oxide film formed for the thinning process, partially lifted off in removal of the oxide film to be particles, and suspended in etching solution. This in turn prevents defective formation of semiconductor elements due to the presence of particles, leading to improved production yield. Further, the protective oxide film is formed by using an ion implantation method and grown by annealing, as well as the buried oxide film. Therefore no extra devices nor extra process steps are required for the formation of the protective oxide film, suppressing an increase in production cost due to the application of the present invention.
According to the semiconductor substrate processing method of the eighth aspect of the present invention, the formation of the buried oxide film and the formation of the protective oxide film are accomplished by separate annealing processes, which provides good controllability for thickness of the individual oxide films.
The semiconductor substrate processing method of the ninth aspect of the present invention provides a semiconductor substrate formed by a bonding method, which has an on-substrate oxide film covered by an SOI layer. In wet etching for thinning the SOI layer, for example, this prevents the problem that the on-substrate oxide film is partially removed and the SOI layer thereon is put in a partially hanging state, thereby preventing exfoliation of the SOI layer and hence formation of particles.
According to the semiconductor substrate of the tenth aspect of the present invention, the doped polysilicon layer is composed of a protective oxide film in the edge part on the first main surface side at least, so that a thin SOI layer is not formed on the buried oxide film in the edge part. In the process of thinning the SOI layer, for example, this prevents the problem that a thin SOI layer is partially surrounded by the buried oxide film and an oxide film formed for the thinning process, partially lifted off in removal of the oxide film to be particles, and suspended in etching solution.
The semiconductor substrate of the eleventh aspect of the present invention provides a specific structure for forming the doped polyisilicon layer with a protective oxide film in the edge part on the first main surface side at least. Further, the doped polysilicon layer is formed also on the second main surface, which can be used as a gettering layer.
The present invention has been made to solve the problems described above, and an object of the present invention is to provide a semiconductor substrate processing method and a semiconductor substrate that can prevent formation of particles from the edge part of the substrate.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.